Mobile users for labeling Mature Content (you may have to update the app)
Settings > general settings > Content you See > scroll down to the bottom
From what I can tell, the filtering is default turned off, so you turn on whatever subject you don’t want to see.
Actually it’s the other way around (because tumblr can’t do anything without being confusing). The Labels are Hide, Blur, and Show. They are defaulted to Hide, so if you want to see mature content, you have to manually set the label to Show.
And if you are under 18, you cannot change the setting until you are 18.
ID: screenshot of tumblr Mature labels on mobile. End ID